The apparatus disclosed herein is specifically designed to spread a mass of sand and/or salt on highways, airport runways and the like; however, it is to be understood that it may be used for spreading fertilizer and other material over areas other than paved surfaces. Such apparatus is not new as is evidenced by U.S. Pat. Nos. to Stewart 2,256,655; Wild 3,744,993; Hallsey 3,232,626; Swenson 3,550,866; Weiss 3,677,540; Heinz 3,756,509; Santer 2,660,439 and 3,768,737. The apparatus shown in the foregoing patents operates to effect uniform distribution by increasing the speed of the conveyor by means of which the material is delivered to the distributor in proportion to any increase in the ground speed of the vehicle. The effectiveness of such apparatus depends upon the conveyor delivering a constant predetermined volume of material. As a practicing matter, the conveyor will not always deliver the same mass for a given speed of the conveyor due to the fact it is a volume system, also the material may cake in the hopper and not flow freely onto the conveyor due to the fact that obstructions such as frozen chunks of salt and sand and/or rocks may hold back the material on the conveyor, so the conveyor will not deliver the required amount of material. Such a system is an "open loop" control since no error signal is derived from the actual material being handled. It is the purpose of this invention to provide a "closed loop" apparatus for delivering a selected mass of material per unit of target area to be covered in spite of such obstructions in the delivery of material to the distributor. Yet other objects are to provide for driver selections of mass to be distributed per unit area, overriding control by means of which the operator may arbitrarily increase the rate of flow to meet an extraordinary ground condition, visual and audible signals to indicate to the driver the failure of flow or depletion and an indicator of the total weight of material distributed at any given time.